Joe Hart no match for four-goal Dries Mertens

Mertens has been pushed into the main striker's role by coach Maurizio Sarri to fill in for missing centre-forward Arkaduisz Milik, who is scheduled to return from a knee ligament injury in January.

The diminutive Belgium forward has seized the day in astonishing fashion for the southerners, who continue to thrive following the departure of 36-goal hero Gonzalo Higuain to Juventus last summer.

Mertens hit three goals in a 5-0 rout of Cagliari last week to add to a goal he scored against Benfica in a 2-1 Champions League win a fortnight ago.

At the San Paolo on Sunday, the 29-year-old completed his hat-trick, including one from the spot, by the 22nd minute as Napoli laid the foundations for a win that moved them up to third place, eight points behind leaders Juventus, at the expense of stuttering AC Milan.

Hart was unlucky not to make contact when Mertens struck a first-time shot from just outside the box on 13 minutes following a well-worked corner by the hosts.

But the Belgian's shot was virtually unstoppable and he was soon on his way to a second after being hauled down from behind in the area.

Mertens promptly stepped up to beat Hart from the spot to double Napoli's lead five minutes later.

Napoli were rampant and after Hart saved twice, including a spectacular one-handed effort at his near post, the 'keeper, racing to get back into position, could only look on as Mertens picked up the rebound from a defender's leg to fire into the roof of the net.

Although Torino came fighting back thanks to Andrea Belotti's strike on the hour, Napoli restored their three-goal advantage when Vlad Chiriches tapped home from Jose Callejon's delivery on 70 minutes.

Toro hit their second, in some controversial fashion only minutes later when Pepe Reina spilled the ball following a free kick by Adem Ljajic to offer up a gift yards from goal.

Although Reina's hands were covering the ball, Luca Rossettini stepped in to kick it away from the Spanish 'keeper and into the net.

Hart did well to deny Marek Hamsik before a goalline clearance kept the Napoli tide at bay.

But Mertens kept his best for last, the Belgian losing his marker in the area before sending a cheeky lob over a rooted Hart and into the net from a difficult angle.

Mertens has now scored eight goals in his past three league games for Napoli, scoring three times in a 5-0 rout of Cagliari last week and once in a 2-1 Champions League win at Benfica.

He has 10 league goals so far this season, two fewer than league-leading Edin Dzeko (Roma) and Mauro Icardi (Inter).

Elsewhere, Antonio Candreva struck a second-half winner as Inter Milan edged Sassuolo 1-0 to hand coach Stefano Pioli his first away victory since he replaced Dutchman Frank De Boer.

Inter's second win in succession following a chastening 3-0 defeat to Napoli a fortnight ago moves the Nerazzurri up to seventh place 15 points off top spot.

Juventus, bidding for a record sixth consecutive league title, moved seven points clear of Roma atop Serie A with a 1-0 win over the capital side on Saturday thanks to a sumptuous 14th minute strike from Higuain.

Lazio will move up to fourth if they beat Fiorentina at the Stadio Olimpico in Sunday's late game.